Tried and tested method for getting kids excited about programming. I started programming with Arduinos when I was 9, and I've taught the basics to kids as young as 5. It's programmed in C++, but it's very easy to learn, with lots of good libraries available.

Very simple dev environment (web browser or smartphone):
- Code visually using Blocks https://makecode.microbit.org/ (or write code using javascript, micropython, c/c++)
- Download compiled binary file to computer
- Upload binary file to the micro:bit (mounts on the computer as a USB drive)
- Or do it all on a smartphone/tablet: write then send code to micro:bit using bluetooth
Can start with just the built-in buttons, led matrix, accelerometer, compass. Then later buy more leds, buttons, servos, whatever as you need them from ebay/aliexpress.
If you're in the US, Microcenter's (http://www.microcenter.com/) have a nice little DIY corner in their shops. I picked up a micro:bit go kit (includes short usb cable, battery, battery holder) for $12 this last weekend. Or buy online for $15 at https://www.adafruit.com/product... or https://www.sparkfun.com/product...